I would like that, when users submit a new topic or posts a reply in a forum, they would be redirected to the topics list.
How can I do this?
There's count of ways to do it, one of these: Rules module. Just add condition on node or comment adding, and add action for redirecting. For taking correct forum page of node or comment, I assume you should enable "php filter" and add php code that got forum taxonomy term and redirect to certain page.